1. Field of the Invention
The invention relates to a method for testing a crystallized semiconductor film, and more particularly such a method for testing a semiconductor film crystallized by irradiating an energy beam. The invention also relates to a device for testing a semiconductor film crystallized by irradiating an energy beam, and a manufacturing method of a semiconductor device including a step of testing a semiconductor film crystallized by irradiating an energy beam.
2. Description of the Related Art
A glass substrate is cheap and easily used in a large size as compared to a conventional single crystalline substrate. Therefore, a technology for forming a semiconductor film on a glass substrate to form a thin film transistor (hereinafter referred to as a TFT) is actively researched and advanced toward the practical use. A crystalline semiconductor film has a better TFT characteristic than an amorphous semiconductor film. As a glass substrate is weak against heat, a laser crystallization is often used for forming a crystalline semiconductor film on a glass substrate as a crystallization method which causes less thermal damage.
In the laser crystallization, a laser beam is used as an energy beam for applying energy to a semiconductor film. The semiconductor film may not be crystallized enough or micro-crystallized depending on the energy density of the laser beam to irradiate. Needless to say, crystallization is most desirably performed at an optimal energy density for crystallization; however, the optimal energy density so far was often dependent on a sensory test.
However, since the sensory test is largely dependent on the operator, quality control of the merchandise is now managed from various angles by digitalizing the crystallization condition by such as Raman spectroscopy, Atomic Force Microscope (AFM), and Total reflection X-ray Fluorescence (TXRF).
However, when the reliability and variation of the data have to be considered to obtain an accurate test result in using any of the aforementioned methods, it takes time for measurement and processing, and a server or a computer is heavily loaded when storing data for testing as the amount of required information is increased.
The optimal irradiation energy density in laser crystallization is quite unstable enough to be changed by the variation in thickness of a semiconductor film or a change in the irradiation atmosphere, further a fluctuation of the output of laser or a change of transmittance of optical system over time. Therefore, in order to perform the laser crystallization under a favorable condition, it is preferable that a substrate as a whole be tested, more preferably tested by in-situ after laser crystallization and the test result thereof be fed back promptly. However, aforementioned method takes too much time for testing, therefore, a prompt test by in-situ cannot be performed. Moreover, the testing and the setting for the optimal energy density themselves could be a delay. In that case, operating rate of the device as well as a producing capacity are drastically decreased.
A laser irradiation system generally costs high for its operation. An XeCl excimer laser used for laser crystallization in particular costs so high that the cost for one-year operation could be enough to purchase another laser irradiation system. Therefore, when the producing capacity is decreased, the cost for operation affects the price of products. It is not preferable in realizing the low price of the products.
Due to the aforementioned problems, the method for testing as described above is not practical enough to be applied to a mass production.
As a method for solving these problems, a method for obtaining a threshold of a micro-crystallization by the luminous intensity of the scattered light of an energy light irradiated on the surface of a semiconductor film after crystallization (Patent Document 1), a method for obtaining an optimal crystallization energy by digitalizing the periodicity of the recessed and projective portions by autocorrelation, which appear on the surface of a semiconductor film after crystallization (Patent Documents 2 and 3), and a method for obtaining an optimal crystallization energy by analyzing the reflected light of an ultraviolet radiation irradiated on a semiconductor film after crystallization from a refractive index or an extinction coefficient (Patent Document 4) and the like are suggested.
[Patent Document 1]Japanese Patent Laid-Open No. 2000-114174[Patent Document 2]Japanese Patent Laid-Open No. 2001-196430[Patent Document 3]Japanese Patent Laid-Open No. 2002-217107[Patent Document 4]Japanese Patent Laid-Open No. 2000-31229